The present invention refers to an apparatus for applying a fluid sample on a substrate, to be preferably used in the medical and chemical field to carry out analyses of a fluid sample with diagnostic scope, preferably for the electro-phoretic test of the fluid sample.
It is known that the result of the electro-phoretic analysis of a fluid sample can be influenced by some factors like the shape, the volume, the amount and the positioning of the fluid sample on the substrate.
Many applicators are known for taking from a tray a little and exactly defined amount, in the order of microliters, of a fluid sample to be transferred on a substrate for the electro-phoretic analysis.
The published patent application WO 97/42496 describes an applicator made of a multiplicity of blades wherein each blade provides a barrier for the fluid sample.
In case the barrier is a physical barrier represented by an aperture, each blade of the applicator takes the fluid sample adhered on its portion of surface comprised between the tip of the blade and the aperture of the blade.
Such an applicator shows some drawbacks.
First, the amount taken of the fluid sample is not exactly defined when the applicator is dipped in the taking tray at such a depth that the barrier made on the blades is exceeded, because in such a case the amount of the fluid sample adhered to the blades over the barrier cannot be foreseen.
The amount of fluid sample taken in such applicator can not be exactly defined also because of the fact that the fluid sample in the taking tray can make a meniscus that can prevent the tip of the blades from getting uniformly wet.
In particular, the trays commonly used for such an applicator are equipped with narrow rectangular marks of housing of the rectangular blades of the applicator where the fluid to be sampled makes a meniscus.
Summing up, if the blades of the applicator are dipped too little in the relative marks of the tray and if the meniscus made from the fluid to be sampled in the relative marks of housing of the taking tray is convex, the risk exists that the central portion of the tip of the blades gets wet while the side areas of the blades stay dry, on the contrary if the blades of the applicator are dipped too much in the relative marks the risk exists that also the portion of the blades over the barrier gets wet.
In both cases the amount of fluid sample taken is not exactly defined. Moreover such an applicator can prevent a complete seeding of the fluid sample taken on the substrate.
As a matter of fact, during the penetration of the blades of the applicator into the substrate, a portion of the fluid sample present on the tip of the blades can be pushed towards the surface of the substrate by the action of the edges of the incision of the substrate and so can stay adhered to the blades of the applicator even after the extraction of the applicator from the substrate.